I would guess that it was B.C. . . . Before Computers.
I had to type my thesis by hand on an old-fashioned Smith Corona electric typewriter. Corrections were made by re-typing the page (no auto correcting typewriters then, and liquid paper was in its infancy and flaked right off the page).
She may have decided it wasn't worth retyping the page.
When I started to work at the university, IBM Selectrics were all the rage. It was a wonderful machine. We copied articles on a machine that made purple ink copies. My fingers were always a mess, and we had to collate by hand. What a lot of work. But even with the copier and all the computers, I was still just as busy, perhaps more. I really loved being a secretary but it was intense at times. Having to type things over again was a pain but I was still good at it and didn’t have to type over much. We did have liquid paper but even that didn’t look very nice. Ah, good memories.